1. Field of the Invention
The present invention related to a display device, especially, to a color liquid crystal display device employing a guest-host (GH) mode.
2. Related Art
With dissemination of digital information, importance of a display for displaying digital information (hereinafter referred to as “electronic paper”) has been growing. Electronic papers are required to have a high level of visibility and a low consumption of electric power. A high level of visibility means a white background close to paper, and, for this purpose, there is preferred a manner based on a scattering white background similar to that in case of paper. Also a reflective displaying manner is advantageous from view of lower consumption of electric power, in comparison with a self-light-emitting display manner. Various manners have been proposed for the electronic paper, such as a reflective liquid crystal displaying, an electrophoretic displaying, a magnetophoretic displaying, a dichroic gyrating ball, an electrochromic displaying and a leucothermal displaying manners. However, none of these manners gives a high level of visibility as required, and an improvement has been desired.
Various types of liquid crystal device (liquid crystal display device) have already been proposed, among which a liquid crystal device employing GH mode is capable of highlight display and is expected as a reflective display. The liquid crystal device employing a GH mode usually comprises a cell filled with a liquid crystal composition, prepared by dissolving a dichroic dye in a nematic liquid crystal, and when a voltage is applied to the cell sufficient to rotate the liquid crystal molecules, the dye molecules rotate along with the liquid crystal molecules and allow changing of light absorption by the cell to thereby effect display. Such a liquid crystal device employing a GH mode, can display images without polarizing plates, is expected as a brighter display in comparison with the prior liquid crystal displays comprising polarizing plates.
As one example of a color liquid crystal display employing a GH mode, a display device comprising three liquid crystal layers is disclosed in JPA No. hei 11-265157 (the term “JPA” as used herein means an “unexamined published Japanese patent application (Kohkai Tokkyo Kohou)”). Each of the three layers, comprising liquid crystal microcapsules and showing an absorption peak at a different wavelength, is individually driven by thin-film transistors with an active matrix system. According to JPA No. hei 11-265157, each of the three layers is individually driven electrically, and, thus, it is necessary to form through-holes. And such a display device suffers from its complicated device configuration, from its complicated production process and from it's high cost.
A liquid crystal optical modulation element comprising a plural of liquid crystal layers is disclosed in JPA No. 2001-33805. Each of the layers, comprising a different liquid crystal composition, modulates light at a specified wavelength. According to JPA No. 2001-33805, the element, employing a simple matrix configuration, is driven with a passive matrix system. And, according to such a system, the contrast of images, especially large size images, is lowered due to crosstalk.
An element employing a GH liquid crystal layer comprising a yellow domain, a magenta domain and a cyan domain, which are disposed in parallel on a substrate, is disclosed in JPA No. hei 9-244070, especially in Example 7 and FIG. 12. Such an element suffers from a low color concentration in a black state or in each color (yellow, magenta, cyan, red, green or blue) state.
And, thus, it is required to develop a multi-color or full-color display device, having a simple configuration, capable of displaying bright images.